Transcriptomic Profiling of Heat-Treated Oriental Lily Reveals LhERF109 as a Positive Regulator of Anthocyanin Accumulation

Pink-flowered Oriental lily cultivars exhibit significant color fading under high temperatures, but the underlying regulatory mechanisms remain unclear. We subjected ‘Souvenir’ Oriental lily plants to temperature treatments (20 °C and 35 °C) and performed transcriptome sequencing and weighted gene co-expression network analysis (WGCNA). The high temperature (35 °C) significantly reduced the anthocyanin content in tepals. The transcriptome analysis identified 8354 differentially expressed genes, with the GO and KEGG analyses revealing a dynamic transition from early stress responses to metabolic adaptation. The WGCNA revealed a module strongly correlated with the anthocyanin content, from which we constructed a gene co-expression network using known anthocyanin-related genes, including the key transcription factor LhMYB12 and structural genes involved in the anthocyanin biosynthetic pathway (LhANS, LhDFR, LhUGT78, and LhF3′H). Through this comprehensive network analysis, we successfully identified and screened LhERF109 as a promising regulatory candidate. The transient overexpression of LhERF109 was found to enhance anthocyanin accumulation and upregulate biosynthetic genes including LhMYB12, while silencing LhERF109 expression produced the opposite effects. These findings identify LhERF109 as a positive regulator of anthocyanin biosynthesis under high temperatures, providing new targets for breeding heat-tolerant lilies with stable flower coloration.